A distinction is made among ball and socket joints between axial joints and radial joints. This distinction depends on the particular direction of action of the forces acting on the ball pivot. The position of the non-deflected ball pivot is used as a reference for this definition of the different ball and socket joints. Accordingly, the principal load on an axial joint is in the direction of the central longitudinal axis of the ball pivot, whereas the principal load in a radial joint acts at right angles to the central longitudinal axis of the ball pivot. Thus, these types of joints differ fundamentally from one another regarding the loads acting on them and hence also regarding the design. In particular, the design of the housing and the material that can be used for the housing are different.
Thus, one peculiarity of axial joints is that the ball pivot with its joint ball is mounted in the housing such that it cannot be separated from the housing during loading along its central longitudinal axis, i.e., in the axial direction. This so-called extraction force of the axial joint is a decisive variable and an essential quality criterion of an axial joint.
In radial joints, the ball pivot is loaded by forces that act on same radially in relation to its central longitudinal axis. As a consequence of this, the extraction force of the ball pivot is lower than in axial joints, which has a decisive effect on the design of the housing.
Regardless of the type of construction of the ball and socket joint in question, considerable efforts are made to make it possible to manufacture these joints at a low cost. Complicated machining operations are to be avoided on the joint to be manufactured as much as possible.
An axial joint as well as a process for mounting such an axial joint are described for this reason in DE 197 55 020 A1. The axial joint comprises a one-piece metallic housing, which is open on one side and through the opening of which a ball pivot can be inserted into an interior space of the housing, the joint ball of the ball pivot being mounted pivotably and rotatably in a bearing area of the interior space. A pivot section of the ball pivot, which section is connected to the joint ball, protrudes from the housing through the opening of the housing. The ball pivot is fixed within the housing by cold forming the edge area of the opening of the housing in the ball pivot. A bearing shell, which is preferably manufactured from a plastic-metal composite, is arranged between the joint ball of the ball pivot and the interior space of the housing. The bearing shell, which has a regular cylindrical opening cross section for inserting the joint ball before the deformation of the edge area, is also deformed by the deformation of the edge area of the opening of the housing such that this opening-side edge area of the bearing shell comes into contact with the joint ball. As a consequence of the simple design of the housing, it is possible to manufacture the housing for this axial joint as a whole by a cold forming process. This axial joint can be produced very cost-effectively as a result.
Moreover, a radial joint, which is manufactured as a whole by a cold forming process, is known from DE 195 36 035 A1. However, this radial joint has a housing that is open on both sides, so that machining of the contact area of the cover is necessary. In addition, the radial joint has a straight shaft of a very simple shape. However, if, for example, the housing has a shaft with a bend or if other geometric shapes of the housing are necessary, the cold forming process will soon reach its limits. Moreover, the cold forming process requires a relatively soft material, and, for example, a steel material of low strength, such as C45, is therefore used in order to manufacture a housing out of it. This low strength of the housing material must be compensated by design measures. However, this means an increased use of material and consequently also increased weight of such joints.
A cold forming process cannot be used for radial joints if these have a highly complicated housing geometry and, because of the installation conditions in the motor vehicle, a shaft with great radii of curvature. For this reason, such radial joints have hitherto been manufactured by means of a hot forming process and are subsequently to be processed by machining at a great effort in order to produce, for example, the interior space for inserting the ball pivot and to prepare the connection area for fastening the cover, which is needed to close the housing, or to prepare a groove for accommodating a sealing bellows edge at the joint housing. Considerable costs arise, which make the manufacturing process needlessly expensive, due to the fact that a plurality of machining operations and, moreover, a plurality of chucking operations in the machining unit are necessary for finishing a housing blank prepared by a hot forming process for a radial joint. This essential drawback for the hot forming process was already described in DE 195 36 035 A1. Steels such as 30MnSiV6, which have a substantially higher strength (approx. 950 N/mm2) compared to the material C45 mentioned before, can be considered for use as materials for radial joint housings that are manufactured by means of a hot forming process.
Since radial joints used hitherto, such as those disclosed in DE 195 36 035 A1 as well, usually have a housing that is open on both sides, the side of the housing located opposite the opening must be subsequently closed with a cover. For example, mechanical damage to the cover area during the use of such a radial joint may cause corrosive media, such as brines, to produce rusting in the area of the cover during operation of the motor vehicle in the winter. However, this may cause leakage and hence failure of the radial joint. Therefore, even though housings open on both sides have hitherto been necessary in radial joints, they do have drawbacks. This is compounded by the circumstance that the machining of the cover support surface and the machining of the opening arranged opposite for inserting the ball pivot as well as of the area in which the edge of the sealing bellows is to come into contact with the housing require a plurality of consecutive chucking operations for machining the radial joint housing. This time-consuming rechucking of the workpiece is likewise associated with corresponding manufacturing costs, which are not desirable.